1. Field of the Invention
Embodiments of the present invention generally relate to an apparatus for supporting a tubular.
2. Description of the Related Art
The handling and supporting of tubular pipe strings has traditionally been performed with the aid of a wedge shaped members known as slips. In some instances, these members operate in an assembly known as an elevator or a spider. Typically, an elevator or a spider includes a plurality of slips circumferentially surrounding the exterior of the pipe string. The slips are housed in what is commonly referred to as a “bowl”. The bowl is regarded to be the surfaces on the inner bore of the spider, an elevator, or another tubular-supporting device. The inner sides of the slips usually carry teeth formed on hard metal dies for engaging the pipe string. The exterior surface of the slips and the interior surface of the bowl have opposing engaging surfaces which are inclined and downwardly converging. The inclined surfaces allow the slip to move vertically and radially relative to the bowl. In effect, the inclined surfaces serve as wedging surfaces for engaging the slip with the pipe. Thus, when the weight of the pipe is transferred to the slips, the slips will move downward with respect to the bowl. As the slips move downward along the inclined surfaces, the inclined surfaces urge the slips to move radially inward to engage the pipe. In this respect, this feature of the spider is referred to as “self tightening.” Further, the slips are designed to prohibit release of the pipe string until the pipe load is supported and lifted by another device.
In the makeup or breakup of pipe strings, the spider is typically used for securing the pipe string in the wellbore at a rig floor. Additionally, an elevator suspended from a rig hook includes a separately operable set of slips and is used in tandem with the spider. The elevator may include a self-tightening feature similar to the one in the spider. In operation, the spider holds the tubular string at an axial position while the elevator positions a new pipe section above the pipe string for connection. After completing the connection, the elevator pulls up on and bears the weight of the string thereby releasing the pipe string from the slips of the spider therebelow. The elevator then lowers the pipe string into the wellbore. Before the pipe string is released from the elevator, the spider is allowed to engage the pipe string again to support the pipe string. After the weight of the pipe string is switched back to the spider, the elevator releases the pipe string and continues the makeup or break out process for the next joint.
Slips are also historically used in a wellbore to retain the weight of tubular strings and aid in locating and fixing tubular strings at a predetermined location in a wellbore. Packers, liner hangers and plugs all use slips and cones, the cones providing an angled surface for the slip members to become wedged between a wellbore wall and the tubular string and ensuring that the weight of the string is supported.
New oil discoveries require drilling deeper wells, which means that spiders and elevators must support heavier pipe strings without crushing the pipe. This slip-crushing issue limits the length of the pipe string that can be suspended by the slips. Uneven axial distribution of the radial slip load on a pipe string exacerbates the slip crushing issue. Therefore, there exists a need in the art for a slip assembly or a spider which more evenly distributes the stress on a tubular along the contact length of the tubular.